1. Field of the Invention
The present invention relates to an ink-jet head for discharging liquid through an orifice and for forming droplets, an ink-jet head substrate, and a method for making the head.
2. Description of the Related Art
Japanese Patent Application Laid Open No. 54-51837 discloses an ink-jet recording process, which is different from other ink-jet recording processes. That is, thermal energy is applied to liquid. The heated liquid forms a bubble, and a force generated by the formation of the bubble discharges a droplet of the liquid through an orifice at the tip of an ink-jet head. The droplet adheres on a recording medium to record information.
The ink-jet head used in this recording process has a liquid-discharging section having an orifice for discharging droplets and a liquid channel provided with a heating section for imparting thermal energy to the liquid, an exothermic element as an electrothermal transducer which generates pressure capable of discharging ink, electrodes for applying electrical energy, and a substrate for holding these components. The head has a heat-accumulating layer provided between the exothermic element and the substrate, and an upper protective layer for protecting the exothermic element and the electrodes from ink.
Japanese Patent Application Laid-Open No. 59-194866 discloses an organic topmost layer formed on an upper protective layer, that is, a surface layer of the substrate. Tthe organic layer has small amounts of pinhole defects and has high coverage, although the layer does not have thermal resistance. Organic materials proposed as the surface layer of the substrate are silicone resins, fluorinated resins, polyamide resins, polyimide resins, epoxy resins, phenol resins, Zirox resins, triazine resins, and BT (bismaleimide-triazine) resins. Among these, polyimide resins are generally used since the resins can readily form films and have high ink resistance.
In recent ink-jet processes, use of various types of paper, for example, plain paper, is required. Thus, inks used in these processes have inherent properties which are different from that of conventional inks. Such inks readily spread on plain paper to decrease the print density compared with coated paper. The dye content in the ink must be increased to enhance the print density. The ink having a high dye content prompts precipitation or adhesion of the dye at a nozzle tip. Thus, urea as a humectant is added to the ink having a high dye content so that the dye does not adhere.
A head containing a urea-containing ink which is designed based on the above-described concept will break down after a long continuous operation. In the head, at failure, the polyimide resin layer on the substrate surface is lost. Thus, the polyimide resin is unsuitable for urea-containing inks. Accordingly, required organic resins must facilitate formation of films, and must have high resistance against urea-containing inks and thermal resistance.
In addition, inks capable of recording on various media, other than plain paper, are desirable. Furthermore, alkaline inks will be developed in future, instead of conventional neutral inks. Thus, ink-jet recording systems must allow use of a wide variety of inks.
Japanese Patent Application Laid-Open No. 61-154947 discloses a method for making an ink-jet head, in which a solid layer having a channel pattern is formed on a substrate, a material for forming a channel is provided thereon, and then the solid layer is removed. When a positive resist is used as the patterned solid layer and when an epoxy resin is used as the ink channel component, an aqueous inorganic or organic alkaline solution or a polar solvent is used to remove the positive resist. Use of a metallic material, such as aluminum, in the substrate and the top board has heat accumulation and material cost advantages compared to Si substrates. Such a metallic material may be dissolved in the aqueous inorganic or organic alkaline solution. Thus, use of a polar solvent such as ethyl cellosolve (ethylene glycol monoethyl ether) is preferable.
Since organic polar solvents dissolve polymeric compounds not soluble in nonpolar solvents, the use of organic polar solvents in production of ink-jet heads will form cracks and voids in the organic layer on the substrate surface or will completely dissolve the organic layer. Accordingly, the material used as the surface layer of the substrate must have resistance against a solution for removing the positive resist, in addition to resistance against the alkaline ink.
Accordingly, it is an object of the present invention to provide an ink-jet head substrate having a stable surface layer which is highly resistive against alkaline inks and polar solvents.
It is another object of the present invention to provide an ink-jet head.
It is still another object of the present invention to provide a method for making an ink-jet head.
An aspect of the present invention is an ink-jet head substrate including a thermal effect section for applying thermal energy to liquid to form a bubble in the liquid, the thermal effect section being connected with a nozzle for discharging the liquid, an electrothermal transducer for generating the thermal energy, and a pair of electrodes, wherein a resin layer composed of a polyether amide is formed on the surface of the substrate.
Another aspect of the present invention is an ink-jet head including a nozzle for discharging liquid, a liquid channel connected with the nozzle, a substrate having a pressure-generating element for discharging the liquid, the liquid channel including the pressure-generating element, and a liquid channel component bonded to the substrate to form the liquid channel, wherein the substrate has a resin layer comprising a polyether amide resin at the bonded section to the liquid channel component.
A third aspect of the present invention is a method for making an ink-jet head including a nozzle for discharging liquid, a liquid channel connected with the nozzle, a substrate having a pressure-generating element for discharging the liquid, the liquid channel including the pressure-generating element, and a liquid channel component bonded to the substrate to form the liquid channel, the method including the steps of forming a polyether amide layer on the pressure-generating element of the substrate, forming a liquid channel pattern on the polyether amide layer using a soluble resin, forming a covering resin layer for forming a liquid channel wall on the liquid channel pattern, forming the nozzle in the covering resin layer above the pressure-generating element, and dissolving the liquid channel pattern.
In the ink-jet head, the liquid channel component may be a top board having a groove for forming a part of the liquid channel.
The top board may be pressed and fixed to the substrate by an elastic member.
The ink-jet head in accordance with the present invention may be of an edge shooter type and of a side shooter type.